ARM: stm32: Kconfig: introduce MACH_STM32F769 flag

This patch introduces the MACH_STM32F769 to make possible to only select
STM32F769 pinctrl driver.

By default, all the MACH_STM32Fxxx flags will be set with STM32 defconfig.
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/mach-stm32/Kconfig

@@ -25,6 +25,11 @@ config MACH_STM32F746
 	depends on ARCH_STM32
 	default y
 
+config MACH_STM32F769
+	bool "STMicroelectronics STM32F769"
+	depends on ARCH_STM32
+	default y
+
 config MACH_STM32H743
 	bool "STMicrolectronics STM32H743"
 	depends on ARCH_STM32